Can I compare a dynamically created object to a type, to see if it conforms? | TypeScript Community | Page 1

willow wagon Oct 16, 2024, 7:11 AM

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Stupid newbie question.
But if I have an object that I dynamically build up, with some required fields, and some optional fields, but then at the end I want to assert of it conforms to a more strict type. Is that possible?

willow wagon Oct 16, 2024, 7:47 AM

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Lets say I have this type, that I build up using a builder pattern, I guess.

interface CDRatorSignupRequestDTO {
    productConfigurationCode: string;
    serviceType: string;
    existingAccountId?: string;
    existingBillingGroupId?: string;
    subscriptionOwnerIndex: number;
    billingGroupOwnerIndex: number;
    accountOwnerIndex: number;
    billingAddressIndex: number;
    accountInformation?: {
        accountTypeId: string;
    }
    billingGroupInformation?: {
        invoiceTypeId: string;
        customAttributes?: {
            ADYEN_SHOPPER_REFERENCE: {
                type: string;
                value: string;
            }
        }
    }
    users: SignupUser[];
    rechargeTicket?: {
        expMonth?: string;
        expYear?: string;
        lastDigits?: string;
        creditCardType?: string;
        rechargeTicketTypeKey: "BALANCE_BASED";
        ticketValue: string;
    }
    optionTransformations: {
        optionKey: string;
        type: string;
    }[];
    campaigns?: {
        campaignKey: string;
    }[];
    consentInformation: {
        consents: {
            textId: string;
            selected: boolean;
        }[];
    };
    anumber?: {
        anumber: string;
        reservationToken: string;
    };
    anumberImportRequest?: {
        phoneNumber: string;
    };
}

Can I somehow in the end, assert that it fits the shape of this type:

type ExistingUserSignup
    = RequiredDTOFields
    & Pick<CDRatorSignupRequestDTO, "existingAccountId" | "existingBillingGroupId">
    & CDRatorSignupRequestWithExclusivePhonenumber
    & { users: { id: string }[] };

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I think my problem might be that this function makes the whole thing fall apart:

const addPhoneNumberToSignupRequest = (request: CDRatorSignupRequestDTO, payload: Payload): CDRatorSignupRequestDTO => {
    if (payload.anumber !== undefined) {
        return { ...request, anumber: { anumber: payload.anumber.anumber, reservationToken: payload.anumber.reservationToken } }
    } else {
        return { ...request, anumberImportRequest: { phoneNumber: payload.anumberImportRequest!.phoneNumber } }
    }
}

dire atlas Oct 16, 2024, 9:45 AM

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willow wagon Lets say I have this type, that I build up using a builder pattern, I guess. ```...

with the builder pattern you could specify what the new type is at each step

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but it kinda sounds like you're asking about runtime checks? types don't exist at runtime, so that's not possible unless you're using runtime types like zod or whatever

willow wagon Oct 16, 2024, 10:01 AM

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Yeah, I guess it would kinda have to be runtime, but I would like it to be compile time 😩

willow wagon Oct 16, 2024, 10:39 AM

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willow wagon I think my problem might be that this function makes the whole thing fall apart:...

This one seems to be the culprit. TS doesn't seem to know that one of those is set, though I'm not sure.

dire atlas Oct 16, 2024, 11:12 AM

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you'll probably need a union there

willow wagon Oct 16, 2024, 11:45 AM

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I think I tried that as well. Problem is the request, need either a field named anumber or a field named anumberImportRequest. Im not well versed in TS to solve that. But I guess I could take the main type, and then extend it with one of the two fields, as a union?

dire atlas Oct 16, 2024, 11:46 AM

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yeah Required & (Option1 | Option2)

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instead of a bunch of optionals that would imply you might have neither

willow wagon Oct 16, 2024, 12:03 PM

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Going back to the bilder pattern stuff… I think I need to solve it that way, because now I have trouble with another type not being set correctly.
It’s hard to explain for me, but I need to for example also set a user, which also can be two things. But if I fix the return type and the input types of my builder functions I have to call them in an exact order. Is there a way to do it, so I don’t have to do that, wit generics maybe, but still type safe?

dire atlas Oct 16, 2024, 12:35 PM

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But if I fix the return type and the input types of my builder functions I have to call them in an exact order.
no, you don't

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you can just add to the building object

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that aside; maybe consider using a DU for the "one of" properties?

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instead of

type NumberData = {
    anumber: {
        anumber: string;
        reservationToken: string;
    };
} | {
    anumberImportRequest?: {
        phoneNumber: string;
    };
};
```use
```ts
type NumberData = {
  anumber: {
    type: "reserved";
    data: string;
    token: string;
  } | {
    type: "import";
    phone: string;
  };
};

willow wagon Oct 16, 2024, 12:40 PM

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dire atlas you can just add to the building object

Can you expand on this one?

dire atlas Oct 16, 2024, 12:44 PM

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here's a really simple example:

hollow widgetBOT Oct 16, 2024, 12:44 PM

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that_guy977#0

Playground Link

Preview:```ts
const building = {}
// ^?

function defineX<T>(building: T): T & {x: number} {
return {...building, x: 0}
}

function defineY<T>(building: T): T & {y: number} {
return {...building, y: 0}
}

const r1 = defineX(building)
// ^?
const r2 = defineY(r1)
...```

dire atlas Oct 16, 2024, 12:44 PM

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if you were mutating it, you could also use asserts

hollow widgetBOT Oct 16, 2024, 12:45 PM

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that_guy977#0

Playground Link

Preview:```ts
const building = {}
// ^?

function defineX<T>(building: T): asserts building is T & { x: number } {
building.x = 0;
}

function defineY<T>(building: T): asserts building is T & { y: number } {
building.y = 0;
}

defineX(building)
building
// ^?
...```

willow wagon Oct 16, 2024, 1:54 PM

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Ah awesome, thank you very much, I’ll see if I can figure it out!

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!resolved

willow wagon Oct 18, 2024, 6:19 AM

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!unresolve

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@dire atlas Sorry, I have another question 😄
I have this stupid if clauses, that, as far as I can see, does so that I have to mutate an object, while doing the builder thing, instead of being able to return a new object, with a specifcied type... something like this:

 // initial signup dto
        let dto = createDefaultSignupDTO();
        //
        // productKey
        dto = addOptionTransformationToSignupDTO(dto, payload.productKey, "SELECTION");

        // campaign
        if (payload.subscription.campaign) {
            dto = addCampaignToSignupDTO(dto, payload.subscription.campaign.code);
        }

The stupid campaign if clause does so I can't be sure what type I return. Is there any way out of that?

dire atlas Oct 18, 2024, 6:26 AM

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use a union or an optional for that extra campaign thing, i guess

willow wagon Oct 18, 2024, 6:31 AM

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Im not sure I follow. I have a few of those optional things, and does that mean I need a union for each one of those? Seems very unwiedly

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I mostly want to be able to do something like
const withCampaign = addCampaigmToSignupDTO and be able to pass that on to the next builder function. But only if it should be added. But I guess I can't do taht, right? Unless I nest a lot of if elses

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Aah hold on, maybe I understand

dire atlas Oct 18, 2024, 6:34 AM

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dire atlas instead of ```ts type NumberData = { anumber: { anumber: string; ...

see this example

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if you have a "one of" kind of relation between properties, a union will let you enforce that "one of", and a DU will further let you enforce "exactly one of"

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but if it's just a singular optional, you could just use an optional for that, a union would be like {} | { maybePresent: string }

willow wagon Oct 18, 2024, 6:36 AM

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Roger, cheers - I will mull it over a bit, see if I can get it to make sense in my head 😄

willow wagon Oct 18, 2024, 2:19 PM

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Thanks again, will resolve!

#Can I compare a dynamically created object to a type, to see if it conforms?